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Author: Subject: Exothermic decomposition of potassium chlorate
SupFanat
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[*] posted on 26-4-2015 at 22:10
Exothermic decomposition of potassium chlorate


Some Russian sources say that potassium chlorate can violently decompose to potassium chloride and oxygen even without adding any fuel to it. Can this reaction be safely reproduced? Does this apply to potassium bromate as well?
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[*] posted on 27-4-2015 at 05:03


It decomposes on heating, but unless a catalyst or fuel is present, I wouldn't call it violent.



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[*] posted on 27-4-2015 at 05:44


That's a common use of potassium chlorate: a convenient source of oxygen in the lab. Just heat the solid and it decomposes with release of oxygen. It's very sedate, really. In my experience it must be melted and it appears to boil, but that's just oxygen being released. Heat it long enough and it re-solidifies as KCl is formed (which has a much higher melting point). I do this all the time for the 'screaming gummy bear' demo for kids. I can't say for sure, but I imagine it would work similarly with bromate.
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[*] posted on 27-4-2015 at 06:03


Oxygen generation is best achieved with heat AND MnO2 as a catalyst.

Merely heating (at the proper temperature for the proper time) converts PURE Na or K Chlorate to Perchlorate.

REF: AD003174

4 NaClO3 --> 3 NaClO4 + NaCl (simplified)

Reality is about 12% remains as unconverted, and some oxygen is liberated leaving NaCl behind.

NaClO3 --> NaClO4 conversion runs about 80% efficient, KClO3 --> KClO4 checks in at about 83%.

[Edited on 27-4-2015 by Varmint]
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[*] posted on 27-4-2015 at 06:52


Quote: Originally posted by Cheddite Cheese  
I wouldn't call it violent.
Actually the right catalyst keeps the reaction going at a slow, steady rate. Heating sodium chlorate is more dangerous than potassium, first it melts, then begins to covert to chloride and the much more stable 7th oxidation state, as perchlorate (a misnomer). During this steps it does evolve some oxygen, but not much. After this if heating persists it explodes. Same goes for potassium, except it takes more heat to explode.



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[*] posted on 27-4-2015 at 07:29



By exploding you mean splattering all over the place not an acutal detonation of some sort?
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[*] posted on 27-4-2015 at 07:54


No, it's an actual detonation. It must be heated quickly, else it will just decompose, also confinement makes it far more likely to explode.



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[*] posted on 27-4-2015 at 12:54



How quickly?
I might try this with a some Na Chlorate at the bottom of a test tube and an oxy acetylene cutting torch.

Will be standing well back.
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[*] posted on 27-4-2015 at 13:59


As fast as possible. An oxy-acetylene torch will work fine. How about not using glass? A steel plate would be much safer.



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[*] posted on 27-4-2015 at 13:59


Some comments from Atomistry (based on extracts from historical chemical journals) on heating pure KClO3 (link: http://potassium.atomistry.com/potassium_chlorate.html ), to quote:

"When heated to 357° C., potassium chlorate undergoes no perceptible decomposition, but the particles cake together, and under the microscope exhibit signs of incipient fusion. At a slightly higher temperature the salt melts, and there is rapid evolution of oxygen between 370° and 380° C., several reactions being initiated.

Potassium perchlorate is formed by autoxidation, the exothermic reaction corresponding with the equation

KClO3 + 3KClO3 = 3KClO4 + KCl + 61.3 Cal.

Scobai has proved the reaction to take place in accordance with this equation by measuring the velocity of formation of potassium perchlorate at 395° C., and has also demonstrated its quadrimolecular nature.

Simultaneously, a unimolecular reaction occurs, potassium chlorate decomposing with formation of potassium chloride, and evolution of oxygen:

2KClO3 = 2KCl + 3O2.

A sufficient rise in temperature initiates the decomposition of the potassium perchlorate, chiefly in accordance with the equation

KClO4 = KCl + 2O2;

and at 445° C. there is complete decomposition in the sense indicated, except for a small proportion of potassium chlorate simultaneously regenerated.

The decomposition is much facilitated by the presence of certain oxides, such as manganese dioxide. The part played by these agents has been the subject of considerable controversy. Repeated use of the oxide produces no measurable diminution in its activity. The action has been suggested to be entirely mechanical, and analogous to that of sand and other substances in promoting the ebullition of water. On this assumption, all bodies in a fine state of division might be expected to exert a similar influence, a view at variance with the results of experiment. The oxides of metals capable of yielding more than one oxide, such as iron, nickel, copper, and cobalt, facilitate the reaction; but the oxides of zinc and magnesium are without effect. Probably higher and lower oxides of manganese are formed alternately at the expense of the chlorate. In presence of the oxide there is no apparent formation of potassium perchlorate, the manganese dioxide inducing the decomposition of the chlorate into chloride and oxygen at a temperature lower than that necessary for the autoxidation of the chlorate to perchlorate with appreciable velocity."

[Edited on 27-4-2015 by AJKOER]
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[*] posted on 27-4-2015 at 14:36



Steel sounds better that glass.

Perhaps I might try heating to plate to hot and placing some Na chlorate on it.
Then heating to dull red and placing some Na chlorate on it.
Then heating to orange.........
Then white hot..

Perhaps it will be a bit like the nitroglycerine drip clip (if ya seen that)

When ng is dripped on a very hot plate it simply deflagrates.
When dripped onto a dull red plate it detonates.
There was a vid of it on a German site but it's gone dead.
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[*] posted on 27-4-2015 at 14:43


Chlorates won't detonate just by heating unless there's some organic fuel, even in several tens or hundreds of kg quantities(in fact early production of perchlorates used that thermal decomposition process of chlorates), though if I remember correctly decomposition is slightly exothermic. This I tell you from a book on chlorates and perchlorates I've read years ago, they tried many possibilities like putting barrels of chlorate on fire, which cause not a single detonation, I don't know where Molecular Mon. read that it WILL detonate..

[Edited on 27-4-2015 by papaya]
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[*] posted on 27-4-2015 at 18:17


Hmm, I didn't try it myself, so I can't say for certain. It sounds like you know better than me. I can't even find the source I derived that tidbit, perhaps it was wrong.



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[*] posted on 28-4-2015 at 02:50



Dam.
There goes by project up in smoke.
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[*] posted on 28-4-2015 at 20:35


Two words PEPCON disaster. However that was ammonium perchlorate not
potassium perchlorate or chlorate. Ammonium chlorates is a very sensitive
explosive. Perhaps that is where the misperception is happening. Now add a
fuel and confinement and an explosion is definitely possible. This happened
on the ISS.
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[*] posted on 29-4-2015 at 02:25


Does chlorate decomposes or converts into other compound by heating below 100°C? I've got a chlorate solution by heating hypochlorite solution (i think it's a chlorate solution), and on further heating I observe some gases coming out of the solution. Maybe some organic residue catalyzes the decomposition?
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[*] posted on 29-4-2015 at 05:36


It shouldn't, because producing it from bleach requires that you boil the solution which must happen at least around 100 C.
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[*] posted on 29-4-2015 at 09:11


The thermal conversion begins in earnest near and above 70C, the reason Nurdrage (and others I suppose) encourage you to boil until crystals just start to form is the insanely high solubility of NaClO3.
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